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Increasing implementations of renewable energy resources to migrate from fossil fuel based electric power to clean energies have been creating new technical challenges due to their integration into an existing electrical grid. In this research, a power electronic converter based on fuzzy-logic controller is developed to govern the transfer and control of power in a grid-connected residential photovoltaic (PV) system with battery storage. A bidirectional dc-dc converter is designed for power transfer between the loads and the battery. A bidirectional ac-dc converter is used as the interface between the PV array and the electricity grid. The fuzzy-logic controller is designed to meet the user power requirement—with the PV array and the battery sized to meet the critical load requirement on site. The results indicate that the fuzzy-logic-based power conversion helped the system to adjust to off-grid, low-battery, full-battery, and on-grid power conditions. The main merit of the design is simplicity in being able to manage the limited supplies from the grid and the renewable PV installation using carefully sized storage that serves critical loads within specific days of power autonomy.

A hybrid AC/DC microgrid is established with the aim of exploiting numerous types of renewable energy to meet the needs of different loads. The microgrid is decomposed by AC DC sub-grids which are connected by an interlink converter (IC). To maintain the security and reliability of the microgrid, an automatic controller for the interlink converter is needed. In this paper, we propose a Linear Matrix Inequalities (LMI)-based current control method for the interlink converter. As the main features here, the interlink converter permits bidirectional power exchange between both sub-grids when a power&ndash, demand imbalance occurs in one sub-grid regardless of the converter system parameters. Simulations with various filter parameters are performed using the Matlab/Simulink software to validate the effectiveness of the proposed controller. In comparison with the existing Linear Quadratic Regulator (LQR)-based current control, the proposed method is more robust against unknown system parameters and high load perturbation.

This thesis investigates the possibilities for increasing the power conversion efficiency and power density of a single-phase single-stage AC-DC converter with power factor correction capability. Initially, the limitations are investigated for simultaneous increase of power density and efficiency in hard switched bidirectional converters. The switching frequency dependent turn-on losses of the transistors have been identified as the main limiting factor. In order to avoid the increase in total power losses with increasing the switching frequency, a control approach is proposed for achieving zero voltage switching transitions within the entire operating range of a bidirectional converter that utilizes power transistors in a bridge structure. This approach is based on operation in the discontinuous conduction mode with a variable switching frequency. Operation in the discontinuous conduction mode ensures the necessary reversed current that naturally discharges the parasitic output capacitance of the transistor and thus allows this transistor to be turned on at zero voltage. On the other hand, the varying switching frequency ensures that the converter operates close to the zero voltage switching boundary, which is defined as the minimum required current ripple at which zero voltage switching can be maintained. Operation with the minimum required current ripple is desirable as it generates the lowest magnetic core losses and conduction losses within the power circuit. The performance and effectiveness of the investigated approach were initially verified in a bidirectional DC-DC converter. A reliable zero voltage switching was confirmed over the entire operating range of a bidirectional DC-DC converter, as well as the absence of the reverse recovery effect and the unwanted turn-on of the synchronous transistor. In order to justify its usage and demonstrate its superior performance, the proposed zero voltage switching technique was compared with a conventional continuous conduction mode operation which is characterized by hard switching commutations. After successful verification and implementation in a bidirectional DC-DC converter, the investigated zero voltage switching approach was adapted for usage in an interleaved DC-AC converter with power factor correction capability. Comprehensive analysis of the converter's operation in discontinuous conduction mode with a variable switching frequency was performed in order to derive its power loss model. The latter facilitated the design process of the converter's power circuit. A systematic approach for selecting the converter's power components has been used while targeting for an extremely high power conversion efficiency over a wide operating range and a low volume design of the converter. The final result of the investigations performed within the scope of this thesis is the interleaved AC-DC converter with power factor correction capability. Utilization of interleaving allows for increasing the converter's power processing capability, reduces the conducted differential mode noise and shrinks the range within which the switching frequency has to vary. The proposed zero voltage switching control approach was entirely implemented within a digital signal controller and does not require any additional components within the converter's circuit. The experimental results have confirmed highly efficient operation over a wide range of operating powers. A peak efficiency of 98.4 % has been achieved at the output power of 1100 W, while the efficiency is maintained above 97 % over the entire range of output powers between 200 W and 3050 W. Doktorska disertacija raziskuje možnosti za povečanje izkoristka močnostne pretvorbe in gostote moči enofaznega enostopenjskega mostičnega usmernika s korekcijo faktorja moči. Najprej smo preučili omejitve, ki preprečujejo hkratno povečanje gostote moči in izkoristka dvosmernih trdo-preklapljanih mostičnih pretvornikov. Izgube pri vklopu močnostih tranzistorjev, ki so odvisne tudi od stikalne frekvence, prispevajo največji delež k celotnim izgubam mostičnih pretvornikov in posledično predstavljajo največjo oviro za hkratno povečanje gostote moči in izkoristka. Z namenom preprečitve povečevanja izgub pri močnostni pretvorbi z višanjem stikalne frekvence smo predlagali napreden način vodenja pretvornika, s katerim se doseže mehko preklapljanje tranzistorjev pri ničelni napetosti v celotnem območju delovanja enofaznega mostičnega pretvornika. Predlagani način vodenja temelji na obratovanju v nezveznem režimu delovanja in sprotnem prilagajanju stikalne frekvence. Z ustreznim obratovanjem v nezveznem režimu tako zagotovimo povratni tok, ki je potreben za praznjenje izhodnega parazitnega kondenzatorja močnostnega tranzistorja pred njegovim vklopom. Po izpraznitvi parazitnega izhodnega kondenzatorja je možen vklop tranzistorja pri ničelni napetosti. S časovno in bremensko-odvisnim spreminjanjem stikalne frekvence zagotovimo obratovanje na meji preklapljanja pri ničelni napetosti. Slednja predstavlja stikalno frekvenco, pri kateri dosežemo minimalni potrebni povratni tok, pri katerem je mogoče vzdrževati preklapljanje pri ničelni napetosti. Delovanje z minimalnim povratnim tokom je zaželeno z vidika minimizacije izgub v magnetnih jedrih in prevodnih izgub v močnostnem tokokrogu. Podali smo tudi navodila za načrtovanje takšnega načina vodenja, ki bo zagotovil zanesljivo preklapljanje tranzistorjev v mostični strukturi pri ničelni napetosti znotraj celotnega območja delovanja pretvornika. Delovanje in učinkovitost predlaganega načina vodenja je bilo prvotno preverjeno na dvosmernem DC-DC pretvorniku. Potrjeni so bili tako zanesljivi preklopi pri ničelni napetosti kot tudi odsotnost okrevanja notranje diode tranzistorjev in neželenega vklopa. Izvedli smo tudi primerjavo predlaganega načina vodenja v nezveznem režimu z najpogosteje uporabljanim delovanjem v zveznem režimu. Pri slednjem se preklopi tranzistorjev izvedejo pri polni zaporni napetosti. Rezultati primerjave so pokazali, da z uporabo predlaganega načina vodenja s preklapljanjem pri ničelni napetosti dosežemo višji izkoristek močnostne pretvorbe in ugodnejšo ter bolj enakomerno porazdelitev izgub v pretvorniku. Izrazito manjši je predvsem delež stikalnih izgub, ki dovoljuje uporabo manjših komponent za hlajenje in posledično omogoča povečanje gostote moči pretvornika. Izpostaviti je treba tudi dejstvo, da je za delovanje v nezveznem režimu zahtevana manjša induktivnost močnostne dušilke. Takšno induktivnost lahko dosežemo z uporabo manjšega magnetnega jedra, kar nudi možnost za dodatno zmanjšanje dimenzij pretvornika. Po uspešnem testiranju na dvosmernem DC-DC pretvorniku smo predlagali še način vodenja v nezveznem režimu s konstantno amplitudo povratnega toka in spremenljivo stikalno frekvenco, prilagojen za uporabo v AC-DC pretvorniku s korekcijo faktorja moči. V doktorski disertaciji je podrobno predstavljeno načrtovanje obravnavanega močnostnega stikalnega pretvornika, ki je bil tudi izdelan in eksperimentalno preizkušen. Proces načrtovanja je bil usmerjen v doseganje čim višjega izkoristka močnostne pretvorbe s pretvornikom čim manjših dimenzij. Eksperimentalni rezultati potrjujejo izredno visoko učinkovitost delovanja, saj znaša maksimalni izkoristek močnostne pretvorbe 98.4 %. Slednji je dosežen pri izhodni moči 1100 W. Ob visokem maksimalnem izkoristku pa pretvornik odlikuje tudi visok izkoristek v širšem območju delovanja, ki presega 97 % v celotnem območju izhodnih moči med 200 W in 3050 W.

As preocupações com o elevado consumo de combustíveis fósseis e a crescente poluição atmosférica conduziram ao desenvolvimento dos veículos elétricos e dos veículos elétricos híbridos. O crescimento do parque automóvel elétrico levou à necessidade de considerar a sua integração na rede eléctrica, ao nível dos impactos estimados, mas também na sua potencial contribuição para uma gestão inteligente do sistema, funcionando como um buffer da energia produzida, permitindo desacoplar a produção do consumo, e assim melhor a eficiência global. Neste trabalho foi efetuado um estudo relacionado com a ligação bidirecional entre os veículos eléctricos e a rede eléctrica que permitirá o uso das baterias instaladas nos veículos participar nesse apoio à rede, debruçando-se primeiramente sobre o desenvolvimento das baterias que permanecem como elos mais fracos. Utilizando diferentes ferramentas de simulação e de análise de resultados foi depois efetuado um estudo sobre dois sistemas alternativos capazes de implementar o conceito V2G respeitando as restrições do ponto de vista normativo. Os resultados obtidos a partir de uma simulação coordenada entre os programas Simulink/Matlab e PSIM permitiram demostram o bom funcionamento dos 2 sistemas propostos, permitindo ficar com a convicção que o conversor multinível será capaz de proporcionar os resultados desejados com um menor tempo de resposta.

Lithium-ion based battery energy storage system has become one of the most popular forms of energy storage system for its high charge and discharge efficiency and high energy density. This dissertation proposes a high-efficiency grid-tie lithium-ion battery based energy storage system, which consists of a LiFePO4 battery based energy storage and associated battery management system (BMS), a high-efficiency bidirectional ac-dc converter and the central control unit which controls the operation mode and grid interface of the energy storage system. The BMS estimates the state of charge (SOC) and state of health (SOH) of each battery cell in the pack and applies active charge equalization to balance the charge of all the cells in the pack. The bidirectional ac-dc converter works as the interface between the battery pack and the ac grid, which needs to meet the requirements of bidirectional power flow capability and to ensure high power factor and low THD as well as to regulate the dc side power regulation. A highly efficient dual-buck converter based bidirectional ac-dc converter is proposed. The implemented converter efficiency peaks at 97.8% at 50-kHz switching frequency for both rectifier and inverter modes. To better utilize the dc bus voltage and eliminate the two dc bus bulk capacitors in the conventional dual-buck converter, a novel bidirectional ac-dc converter is proposed by replacing the capacitor leg of the dual-buck converter based single-phase bidirectional ac-dc converter with a half-bridge switch leg. Based on the single-phase bidirectional ac-dc converter topology, three novel three-phase bidirectional ac-dc converter topologies are proposed. In order to control the bidirectional power flow and at the same time stabilize the system in mode transition, an admittance compensator along with a quasi-proportional-resonant (QPR) controller is adopted to allow smooth startup and elimination of the steady-state error over the entire load range. The proposed QPR controller is designed and implemented with a digital controller. The entire system has been simulated in both PSIM and Simulink and verified with hardware experiments. Small transient currents are observed with the power transferred from rectifier mode to inverter mode at peak current point and also from inverter mode to rectifier mode at peak current point. The designed BMS monitors and reports all battery cells parameters in the pack and estimates the SOC of each battery cell by using the Coulomb counting plus an accurate open-circuit voltage model. The SOC information is then used to control the isolated bidirectional dc-dc converter based active cell balancing circuits to mitigate the mismatch among the series connected cells. Using the proposed SOC balancing technique, the entire battery storage system has demonstrated more capacity than the system without SOC balancing. Ph. D.

This thesis proposes a new bidirectional three-phase AC-DC power converter using matrix converter and Z-source inverter topologies. Advantages of the AC-DC matrix converter are the inherently controllable power factor, the tight DC voltage regulation, the wide bandwidth with quick response to load variation, the single-stage buck-voltage AC-to-DC power conversion; advantages of the z-source inverter are the increased reliability by allowing the shoot-through between upper and lower power switches of one inverter leg, insensitivity to DC bus voltage due to the extra freedom of controlling DC-link voltage. The proposed Matrix-Z-source converter (MZC) marries up both advantages of AC-DC matrix converter and Z-source inverter. It can achieve voltage-boost DC-AC inversion capable of variable voltage variable frequency (VVVF) AC output; it can achieve voltage-buck AC-DC rectification capable of inherent control over AC current phase angle and DC output regulation with a (VVVF) AC source supply. Both foresaid performance in DC-AC inversion and AC-DC rectification can be implemented in a simple open-loop control manner. Three constraints of VSI, in the bidirectional AC-DC power conversion, are the peak AC voltages are always less than DC-link voltage, closed-loop control has to be employed when DC regulation and/or AC current phase angle control are required, and AC voltage is sensitive to the variation of the DC-link voltage in DC-AC inversion. The voltage-boost inversion and/or voltage-buck rectification of MZC overcomes the first constraint; thus MZC enables the AC machine voltage increased higher than DC-link voltage hence advantages of running AC machine at relatively high voltages are enabled. The direct DC voltage regulation and inherent AC-current-phase-angle control of MZC overcomes the second constraint in an open-loop manner; hence a simplified system design is obtained with sufficient room for the further improvement by closed-loop control schemes. The extra freedom in controlling DC-link voltage of MZC overcomes the third constraint hence a DC source voltage adaptable inverter is obtained. This thesis focuses on the study of the feasibility of the proposed MZC through theoretical analysis and experimental verification. At first, the proposed MZC is conceptually constructed by examining the quadrant operation of AC-DC matrix converter and Z-source inverter. After the examination of the operating principles of both AC-DC matrix converter and Z-source inverter, the configuration of MZC is then proposed. The MZC has two operating modes: DC-AC inversion and AC-DC rectification. Circuit analysis for both operating modes shows that the new topology does not impose critical conflict in circuit design or extra restriction in parameterization. On the contrary, one version of the proposed MZC can make full advantage of Z-source network components in both operating modes, i.e. a pair of Z-source inductor and capacitor can be used as low-pass filter in AC-DC rectification. The modulation strategy, average modeling of system, and features of critical variables for circuit design of the proposed MZC were examined for each operating mode. Simulations of the proposed MZC and its experimental verification have been presented. Analytical models of conduction and switching losses of the power-switch network in different operating mode have shown that the losses in the MZC compare favorably with conventional VSI for a range of power factor and modulation indices.